You can search aquabid by location can find any California breeders. Most will allow you to pick up if you're willing to drive, to save on shipping hassles.

For your tank, bettas like room to swim side to side. Mine ADORES the 20gallon it has to itself for the time being. So if the 28 is longer then the cube, i'd go for it, you can have more tank mates that way as well.

Nothing wrong with that size of a tank for a betta, that is a palace! lol..
The things you want to remember though with using larger tanks, is that some male bettas can have a hard time swimming in larger spaces, at first, until they build up their muscles. Most live their lives prior to you picking them up at a store in half gallons or less. So you will want to make sure your filter is on the lowest setting, or baffled by that way, or using another aquarium sponge in the outflow to help cause less of a current. But in that size of a tank, it shouldn't be too big of a problem as long as he has a lot of surface space that isn't being moved around. You will want to make sure that it is densely planted with medium to tall plants and a hiding spot or two such as a cave. It will help keep his stress levels down some from being in a larger tank.
A tank that size he would be good with other peaceful fish, a group of 5-6 cory cats would be awesome cleaners, and since they are bottom dwellers, your betta won't have an issue with them. Platties, female mollies, guppies are good with them. A tank that size you shouldn't have a problem with the smaller grouping fish such as the different tetras as they are usually mid level. Sometimes in smaller tanks, the small fast fish can fluster and stress out a betta, but a larger tank like that I would imagine they will be fine. But adding in tank mates is your choice, of course =) Just make sure they are mid-lower level swimmers, because others, like gurami's are top dwelling and territorial and will fight with your betta. They are bullies :P

You could also consider doing a DIY dividers and have quite a few in there. Just make sure there is a few inches from the water level to the top of the divider so they won't jump over.

As far as the Nano goes.. I think a member on here has one for his, but other then that, I have no personal knowledge of them.

Thanks for the input. I just went to the local PetSmart with my wife to look at fish, well, just because I could. I was surprised how nice their betta's were, but sadly the little bowls were a bit dirty. My wife suggested I buy all eight they had in stock because she felt sorry for them.

got 2 betta's from there .. and they hand pick the one's they want from the breeders for the store .. so if your looking for specific coloring/finnage .. u can talk to her (she's usually at the cashier i forget her name) and she will call u when she get's them in ..

they get their betta shipments every monday .. call first .. to get first pick .. they run out fast .. usually i don't get to visit till saturday .. so i miss out on all the awesome ones .. and he has good pricing .. he quoted me 4.99 for HM boys

i know this place! but i think the one i'm thinking of is in brea. i didn't mention it because the last time i went, they only had around 4-6 bettas, and they were all half-dead and in dirty water. :/

of course, the stores are probably different because of management, so good for that one!

there is a tong's in brea too .. but it's not the same place or owner .. the funniest thing is they are not affiliated with the tong's in fountain valley at all .. just happen to have the same name .. because we asked the owner (i think his name is henry) .. cus we thought they were a chain store .. but apparently not hehe =D

.. they are slightly over priced there compared to other LFS by a few bucks .. and they just re-designed their freshwater and saltwater tanks .. and plant tanks .. so it looks a lot better now .. more spacious .. i've gotten 2 apple snails from them .. they are very knowledgeable about fish friends .. but not a good place for bettas ..

tongs has been seriously lacking lately .. D= .. it's a shame too since they get their bettas from thailand (according to the guy that works there with the lisp) .. i don't really trust that guy too much ..

i've also found another LFS but it's a bit of a drive and not in OC .. it's called Jan's tropical fish .. and they also get their bettas from thailand .. where i got 3 girls and 1 boy .. that i'm planning to breed ^_^